The present invention relates to a metallurgical plasma melting furnace having burners as starting aids for the plasma burners for the melting of metals and alloys, the furnance being charged predominantly with light scrap.
It is already known to use plasma burners with transferred low-temperature-gas plasma for the melting of metals and alloys. These plasma burners operate in preferably cylindrical furnace vessels and are preferably arranged in openings in the sidewalls of the plasma melting furnace. Since the energy given off by a plasma burner increases with the length of the plasma burner, in the known industrial solutions the scrap is introduced into the furnace in such a manner that the burner lies above the pile of scrap and is not covered by the charge material. This is, in general, only obtained with charge material of high bulk density, so-called coarse scrap. Upon the melting down of scrap of low bulk density, so-called light scrap, practically the entire volume of the furnace vessel must be filled with light scrap upon the charging in order to obtain a sufficient amount of liquid metal after the melting down. As a result of this high level of filling, the plasma burners, if technically reliable operation thereof is to be possible at all, can operate only with strongly reduced output until the scrap has been sufficiently melted away in front of the plasma burner. The reason for operation with reduced output resides in the physical nature of the transferred plasma arc. For a given arc current the arc voltage, and thus the energy converted, are a function of the length of the plasma burner. If the plasma burner cannot be fully formed due to solid material which limits its length, the energy transferred is also limited thereby. Only after the plasma burner has melted down a sufficiently large crater, can it operate with optimum output.
It has furthermore been known to increase the melting power of arc furnaces by using additional liquid or gaseous fuel burners. Practical experience has shown that these additional burners ignite completely independently of the position of the charge material and the degree of covering of the burners and can be operated with maximum burner output. However, there is the disadvantage that these additional burners supply a considerable proportion of the energy required for the melting, so that the advantage of arc furnaces, namely independence from liquid or gaseous fuels, is lost to a great extent.